How frequently must an aircraft be re-weighed?

The requirement for re-weighing an aircraft is specifically tied to changes in its weight and the aircraft's classification. When the weight of an aircraft changes beyond 2% of its empty weight, it necessitates re-weighing to ensure that the current weight is accurately reflected in the aircraft's operating limitations, performance calculations, and weight and balance documentation. This is crucial for maintaining safety standards and ensuring compliance with regulatory requirements.

In addition, for aircraft that have an empty weight of over 12,500 pounds, a re-weighing must be conducted at a maximum interval of every five years, irrespective of whether other changes have occurred. This provision helps ensure that larger aircraft, which may undergo more significant modifications or carry heavier payloads, are consistently assessed for their weight compliance. Thus, the correct answer encompasses both scenarios, ensuring that an accurate and safe weight is maintained for the aircraft's operation.